Because of its strength and stability, zirconium dioxide is widely used in the dental field, for example as framework material for crowns and bridges.
Described in WO 99/47065 A1 is a method for the manufacture of a dental prosthesis, which is based on a zirconium dioxide blank and is to be fitted onto a pre-prepared tooth stump. The blank consists of a pre-sintered zirconium dioxide disk, from which a shape is worked out that corresponds to that of the dental prosthesis, in particular allowing for the shrinkage characteristics during the final sintering stage. The starting powder can contain coloring elements, which are present in oxide form.
Known from WO 2005/070322 A1 is an inorganic/inorganic composite material and a method for the production thereof. In the production of the composite material, one subjects an oxide ceramic powder of ZrO2 (zirconium oxide) to a shaping step and pre-sintering to create an open-pored crystalline oxide ceramic molded part, onto which one applies an infiltrating substance in vacuum at room temperature, and sinters the oxide ceramic to full density under regular air and ambient pressure to create the inorgani/inorganic composite material. These measures are meant to produce an improvement in esthetical appearance.
In order to be able to provide restorations of the desired coloring, one uses raw materials in powder form that contain various coloring elements in oxide form, to create a mixture with a raw material in powder form that consists of non-pigmented zirconium dioxide, i.e. white zirconium dioxide. The zirconium dioxide on principle will be an yttrium oxide stabilized zirconium dioxide powder.
The fact that the coloring elements are uniformly distributed though the mixture created from the raw materials in powder form creates the advantage that the mixture to be pressed has a homogeneous coloring, so that as a result during the subsequent machining of a pre-sintered or possibly even fully sintered blank it will be ensured that the produced dental restoration exhibits the same coloring all over its outside surface and throughout its body. Fundamentally different from this method is an alternative process for coloring a dental restoration. Here, the latter in its completed state is immersed into a coloring solution. Since the penetration of coloring ions decreases with increasing distance from the surface, i.e. one obtains a coloring gradient, one faces the drawback that in cases when a corresponding restoration has to be reworked, different regions may have differing color characteristics. This is equally true of the fluorescence characteristics of a corresponding restoration that contains bismuth ions as the substance generating the fluorescence, as is described in WO 2014/164199 A1.
Known from WO 2015/199018 A1 is a colored translucent zirconium dioxide body that consists of yttrium oxide stabilized zirconium dioxide, erbium oxide, iron oxide, cobalt oxide, or aluminum oxide.
The objective of the present invention is to further develop a method of the above-mentioned type so that the completed restoration not only possesses the desired color but also fluorescence characteristics that at least are close to that of a natural tooth.